1. Field of the Invention
This invention relates to a system and method to improve data transmission performance of a radio frequency (RF) wireless and optical wireless digital communication link by reducing signal degradation due to fading and scintillating channel.
2. Background Information
With the growth of worldwide telecom infrastructure, broadband wireless connectivity via radio and optical frequencies has been considered to be the future of the global telecommunication industry. The communication efficiency associated with transmitting information is known to be dependent upon the signal design, error correction code as well as the characteristics of the transmission medium. While there are advancements in high-speed digital processing in the time domain to remove signal degradations at the receiver, there has been little progress to utilize the additional dimensions in the spatial domain to support data recovery operations.
One approach to mitigate the effects of scintillation is error correction code as shown in U.S. Patent Application Publication No. 20020157060. For example, Reed-Solomon code in conjunction with data interleaver is effective in combating error bursts. The cost is the overhead associated with sending the parity bytes needed for the decoder, latency of decoding operation as well as complexity to implement the codec and interleaving/deinterleaving circuits.
Another approach is to perform repeated transmission until an acknowledgement is received. A detailed operation of this approach is disclosed and described in U.S. Pat. No. 6,043,918. This concept is similar to the reliable transport control protocol (TCP) at the network layer. The challenge is to choose the right duration for the acknowledgement time-out without artificially inducing a data traffic bottleneck due to retransmission.
One other solution is to provide signal strength feedback to the transmitter (described in U.S. Pat. No. 6,285,481). Data transmissions can be suspended until scintillation activities subside allowing signal power to return back to the nominal level. However, link suspension reduces network availability and decreases subscriber satisfaction.
Also, a receiving system with multiple optical detectors is described and proposed in U.S. Pat. No. 6,243,182. The patent shows a spatial combiner scheme to capture optical power lost due to scintillation. However, it does not reveal the critical design in calculating the spacing between detectors and the size of the array needed to accomplish the job of a spatial scintillation equalizer. Furthermore, no temporal equalization is suggested as part of an overall solution to the problem of scintillation.
It is one object of the present invention to provide a system and method to mitigate the effects of fading and scintillation on a radio frequency (RF) and optical wireless signals.
It is another object of the present invention to provide an optimal signal equalization scheme simultaneously in both the spatial and temporal domains.
Yet it is another object of the present invention to perform an optimal recovery of lost transmission power of the wireless signal at the receiver.
Still another object of the present invention to apply space-time sampling as compared to separate spatial or temporal sampling in receiver signal processing.
Still another object of the present invention to apply space-time equalization to single mode time modulated optical communication links for terrestrial wireless and satellite communications.
Still another object of the present invention to apply the space-time equalization to single beam time modulated RF wireless communication links for terrestrial wireless and satellite communications.
Still another object of the present invention to apply space-time equalization to single mode space-time modulated optical communication links for terrestrial wireless and satellite communications.
Still another object of the present invention to apply space-time equalization to multimode space-time modulated optical communication links for terrestrial wireless and satellite communications.
Still another object of the present invention to apply space-time equalization to multimode multi-antenna space-time modulated optical communication links for terrestrial wireless and satellite communications.
Still another object of the present invention to apply space-time equalization to single beam space-time modulated RF wireless communications link for terrestrial wireless and satellite communications.
Still another object of the present invention is to apply space-time equalization to multi-beam space-time modulated RF wireless communication links for terrestrial wireless and satellite communications.
Still another object of the present invention is to apply space-time equalization to multi-beam multi-antenna space-time modulated RF communication links for terrestrial wireless and satellite communications.
Still another object of the present invention is to maximize the throughput of a wireless radio frequency transmission system by using space-time equalization.
Still another object of the present invention is to maximize the throughput of a wireless optical transmission system by using space-time equalization.
Still another object of the present invention is to maximize the throughput of a satellite transmission system by using space-time equalization.